1. Field of the Invention
The present invention relates to exposure apparatuses and device manufacturing methods, and more particularly to an exposure apparatus that exposes an object with an energy beam and forms a pattern on the object, and a device manufacturing method that uses the exposure apparatus.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing electron devices (microdevices) such as liquid crystal display elements or semiconductor devices (integrated circuits or the like), an exposure apparatus such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper), or a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner)) is mainly used.
In this type of exposure apparatus, illumination light is irradiated on a mask (or a reticle) on which a pattern is formed, and the pattern is projected on a substrate (such as a glass plate or a wafer) that is coated with a sensitive agent (resist), via a projection optical system, and thereby the pattern is respectively transferred onto a plurality of shot areas. Then, by overlaying and forming plural layers of patterns on the substrate, the electron device referred to above is manufactured. Therefore, it is necessary to accurately overlay and form a pattern of the mask on the pattern already formed on the substrate. Vibration of the exposure apparatus or the like is a factor that degrades the overlay accuracy. Accordingly, in order to restrain the vibration from the outside such as a floor from being transmitted to the apparatus, an exposure apparatus main body is installed on a plurality of vibration isolation tables (e.g. refer to PCT International Publication NO. 2008/129762). In this case, the vibration isolation table means a member that has a role of restraining transmission of the vibration from the outside of the apparatus (such as the floor) to the apparatus main body, and is also called a vibration elimination table. There are two types of the vibration isolation tables, which are a passive type and an active type.
However, the exposure apparatus is growing in size with the times, and the vibration isolation table is similarly growing in size according to the size increase of the exposure apparatus, which leads to the cost rise. Further, as a vibration isolation table in order to reduce the load placed on the vibration isolation table, a vibration isolation table having a structure in which coil springs are increased in number and the apparatus main body is supported by the coil springs is also known. However, when the stiffness of the vibration isolation table is too high, the vibration isolating effect decreases instead.
Further, the exposure apparatus described in, for example, PCT International Publication No. 2008/129762, or the like is equipped with a plurality of image-forming optical systems. It is usual that the plurality of image-forming optical systems are fixed to (held on) one surface plate (which is called an optical surface plate) because correction of the positional relation among them becomes difficult if some of the plurality of image-forming optical systems are relatively translated or have rotational displacement with respect to the other image-forming optical systems. In order to restrain local deformation of the optical surface plate, typically, the optical surface plate is supported at support points (hinged joint support sections) in a plurality of positions, e.g. three positions that form one plane, on the exposure apparatus main body.
However, the optical surface plate to which the plurality of image-forming optical systems are attached is heavy in weight and has a low stiffness, and therefore, in practice, when the exposure apparatus main body deforms, the hinged joint support sections in three positions are prevented from freely rotating, because of a frictional force caused by the empty weight of the optical surface plate and the plurality of image-forming optical systems, and as a consequence, the optical surface plate locally deforms and the relative displacement (mainly, the relative angle displacement) among the plurality of image-forming optical systems occurs, which degrades the optical performance in some cases. Therefore, a method has been employed in which in order to reduce the resistance by the frictional force at the hinged joint support sections by cancelling a part of the empty weight, helical compression springs are placed near the support points to supplementary support the optical surface plate from the apparatus main body side.
However, since the spring constant of the helical compression spring is comparatively large, there is a risk that the helical compression spring degrades the apparatus performance because the support force of the helical compression spring varies owing to the apparatus deformation, or excites vibration because the helical compression spring has the eigenfrequency.